Singapore Fire Safety Engineering Guidelines 2015_1.pdf

Fire characteristics iv minimum details needed to

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Fire Characteristics (iv) Minimum details needed to describe the fire Heat Release Rate (HRR) HRR per unit area Fire perimeter Elevation from finished floor level Soot yield Heat of combustion Toxic substances (for FED analysis) Radiative heat flux (for FED analysis) The HRR chart is to be included in the FER to demonstrate the fire characteristics. The fire characteristics used in the CFD modelling shall follow the fire hazards identified and design fire(s) established in Table 3.1 of this guideline. Minimum details needed
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26 (v) Selecting the CFD software Given the availability of different CFD models, the FSE is responsible to assess its suitability for use in the fire engineering study. Whilst this set of guidelines is written predominantly for FDS considering its wide use in the fire engineering fraternity in Singapore, they also apply in a similar manner to other CFD models. The list of recognised CFD softwares is as follows: Fire Dynamic Simulator (FDS) Fluent Phoenics Approval from SCDF is required if a CFD software, other than the above, is to be used. The use of any particular CFD software (including its version) must reflected in the FEDB. Selecting the CFD software (vi) Computational domain The computational domain should be as close as reasonably practicable to the actual enclosure. Simplification (such as modelling a slightly curved wall as a straight wall) can be accepted as long as it does not adversely affect outcome of the CFD modelling. Where inlet and/or exhaust vents are located at the domain boundaries, FSE has to include an additional 5m buffer outwards to account for the aerodynamics of the vents. Where wind effects are being modelled, the domain should be extended correspondingly to take this into consideration. Computational domain
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27 (vii) Boundary conditions Assumptions on the type of surface and material properties such as ambient temperature and properties of surfaces must be included. In situations where adiabatic/inert surfaces are assumed, justification on why such assumptions are considered appropriate must be included. Assumptions on ambient temperature & external wind effect for the areas being modelled must be included. As a guide, ambient temperature in air-conditioned spaces can be taken to be 24 o C while that of non air-conditioned spaces, 32 o C. Should other temperatures be adopted, FSE will provide the justifications. Boundary conditions (viii) Mesh and grid resolution The type of meshing i.e. structured vs unstructured and grid resolution can have significant impact on the accuracy of CFD computation, particularly for large eddy simulation models. In the case of FDS, FSE has to state whether single mesh or multi-mesh is to be used. Other information includes screenshots to illustrate the mesh set up, the mesh boundaries and the respective grid resolution. The recommended fine grid resolution should follow the FDS user guide.
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